Kang Han's Sister summary:

For the sake of Kang Hanni's one and only family member, her younger brother, Kang Han, Hanni works hard everyday to earn money. One day, she is informed by his school that if he misses one more day of attendance, he will be expelled. However, after she reprimands him harshly, he runs away from the house.In order to prevent his expulsion, the older sister must dress-up and impersonate as her younger brother and attend school.